The invention relates to the longitudinal compressive treatment of webs in which a stationary retarder surface acts upon a driven web to cause the web to slow and longitudinally compact or crepe in a treatment zone. This technique, sometimes referred to as microcreping because of its ability to produce fine crepes, is exemplified by our prior U.S. Pat. Nos. 3,810,280, 4,142,278 and 5,060,349, which are incorporated herein by reference.
As described in our '349 patent, a particularly-advantageous retarder sheet for a microcreper comprises a large multiplicity of parallel ridges and grooves biased obliquely to the direction of drive of the web. However, in some cases a web treated by such a retarder member, as it passes from the smooth primary surface to the obliquely-grooved retarder surface, may tend to travel at an angle to the feeding direction of the roll, and deform into a parallelogram. The treated web may retain this deformation even after it is wound onto a take-up roll.
Previous methods of correcting this parallelogram deformation have resulted in deformations to the web, for instance stretching that has tended to defeat the purpose of the compressive treatment, or uneven stretching of the web that give the web an undesired, Moire/ textured appearance.